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timer delay?

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Solidacid

Sun Dec 21 2008, 01:00PM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

hey guys.
im trying to build a 10 second(or so) timer.
i need to be ablo to press a switch and 10 seconds later it will activate a relay for a few seconds, then turn off.

i was hoping you could point me in the right direction

im guessing i should be able to do this with a ne555 timer IC, right?

Mads Barnkob

Sun Dec 21 2008, 01:30PM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

here is basicly what you want, just add a reset function that sets your run time and put your start switch in too.

Solidacid

Sun Dec 21 2008, 03:11PM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

looks perfect! ill build it right away :D
thanks :D

Solidacid

Mon Dec 22 2008, 01:43AM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

unfortunatly i was unable to get the circuit to work the way i wanted. but i found This instead.
it's simple and effective.

now i just need to make it only stay on for about 3 seconds and then remain off.

LithiumLord

Mon Dec 22 2008, 02:33AM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Heh, I've got a real madman approach (like I always do)
You have a 555 rigged in an astable mode. Now, you rig it's output through an OR gate to it's RESET. The other input of the OR gate is your control switch. (use that in my SSTC btw). What you get? Whenever you hit the switch, your 555 outs HIGH for 10 seconds and then gives a delay before you can retrigger it. Now how to attach a relay? You just rig a SECOND 555 (can be 556) with it's THRESHOLD pin to the THRESHOLD of the first 555! What do you get? Your primary 555 outs LOW because of the lack of any signal on the OR gate to give it the RESET. However the second 555 outs HIGH as it's rigged to the cap only and it's RESET pin is connected to Vcc. Now, you hit the switch. Like always, your 555 outs HIGH straight off and this acts as a delay-reset RS-trigger. So, while the cap changes it's voltage, both timers out HIGH (first one - because now you've set up it's RESET and second one - just because it keeps doing so). Now, the cap voltage crosses the off-state threshold - both timers out LOW and the cap starts to charge to Vcc as there is no reset so DIS doesn't work. Now, invert the output of the second 555 - it's just what you need! Inverted, it gets HIGH after a delay you've set and remains in that state before the cap recharges. The schematic is really awesome - 556, OR-gate, a single set of cap+2resistors+(if needed) a diode - all like in a generic 555 astable mode - and just one pin of the second half of 556 (the THRESHOLD signal input) is connected to the THRESHOLD of the first one, in order to invert the signal you can either use an inverting circuit or, if your relay can be driven with a single 555, just rig it between Vcc and OUT. That's all! Simple and accurate.

Dylan

Mon Dec 22 2008, 06:14AM

Registered Member #1024 Joined: Sun Sept 23 2007, 10:56AM
Location: Northern NSW, Australia
Posts: 95

Hahhahahaa, LithiumLord , you are a legend!
I love your enthusiasim, and willingness to help everyone, your an asset to the forum!
And Solidacid, all I can say is let us know how LithiumLords idea works out, it sounds good to me!

LithiumLord

Mon Dec 22 2008, 03:29PM

Registered Member #1739 Joined: Fri Oct 03 2008, 10:05AM
Location: Moscow, Russia
Posts: 261

Sorry it was 4:34am here so I forgot that TRIG input of the second 555 has to be rigged there as well. Anyway, that has to work.

rp181

Tue Dec 23 2008, 02:15AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

I tried the last one on that page, and it works somewhat. With mine, the output goes high for a certain amount of time, then goes low. It should do the opposite.

Myke

Tue Dec 23 2008, 07:23AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

You mean go low for a certain amount of time then go high? Just put an NOT gate on the output.

Solidacid

Tue Dec 23 2008, 01:28PM

Registered Member #1430 Joined: Sun Apr 06 2008, 11:12AM
Location: Ã…rhus, Denmark
Posts: 102

thanks for all the input people!

i think im gonna go with this:http://www.circuitdb.com/circuits/id/25 as it is simple, durable and inexpensive.

now im just wondering, can i convert it to work on a 9volt battery instead of 12v?
i tried hooking it up to a 9volt without any modifications and it didn't work.

the point of this circuit is that i want to trigger a relay after a certain amount of time (atleast 10 seconds). when the relay triggers it conducts the current from an old cordless screwdriver battery though about 2 meters of copper wire to about 5 cm of konstantan(pretty much the same as nichrome) wire. and lights my rocket engine.

at first i thought i would run the above mentioned circuit with the 18v battery, but im afraid the circuit might not survive it.
do you think i could just run it off the 18v battery?

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